Pulse generating system for electrostatic precipitator

1. A pulse generating system for generating high voltage pulses to energize an electrostatic precipitator ( 10 ), said system comprising:

A first power supply ( 1 ) and a second power supply ( 2 ), where said second power supply ( 2 ) is arranged to pre-charge said electrostatic precipitator ( 10 ) to a DC voltage;

A storage capacitor ( 7 ) and a series inductance;

A clamping circuit;

A switching device ( 5 ) coupled in parallel with an anti-parallel rectifier device ( 6 ); and

wherein said system is arranged to be coupled to said electrostatic precipitator ( 10 ); characterized in that said switching device ( 5 ) has a gate electrode and that said switching device ( 5 ) has controllable turn-off capability, being controllable by a gate signal supplied to said gate electrode.

2. A system according to claim 1 , characterized in further comprising a transformer ( 9 ) with a primary and a secondary winding, and in that

said first power supply ( 1 ), said storage capacitor ( 7 ), said switching device ( 5 ) and said parallel-coupled anti-parallel rectifier device ( 6 ), are coupled to said primary winding of said transformer;

said second power supply ( 2 ) and a coupling capacitor ( 8 ) are coupled to said secondary winding of said transformer ( 9 ); and

said system is arranged to be coupled to said electrostatic precipitator ( 10 ) via said coupling capacitor ( 8 ).

3. A pulse generating system according to claim 1 , characterized in that:

said first power supply ( 1 ) is connected to one terminal of said storage capacitor ( 7 ), where the other terminal of said storage capacitor ( 7 ) is connected to one terminal of a primary winding of a transformer ( 9 ), and wherein the other terminal of said primary winding of said transformer ( 9 ) is connected to a common terminal,

said switching device ( 5 ) and said anti-parallel rectifier device ( 6 ) are connected in parallel, whereof one terminal of said switching device ( 5 ) is connected between said first power supply ( 1 ) and said storage capacitor ( 7 ) and the other terminal of said switching device ( 5 ) is connected to said common terminal,

one terminal of a secondary winding of said transformer ( 9 ) is connected to the common terminal and the other terminal of the secondary winding of said transformer ( 9 ) is connected to said electrostatic precipitator ( 10 ) via a coupling capacitor ( 8 ), and

said second power supply ( 2 ) is connected to the junction between said coupling capacitor ( 8 ) and said electrostatic precipitator ( 10 ).

4. A system according to claim 1 , characterized in that said switching device ( 5 ) is arranged to be turned off before the instant in time of the natural zero-crossing of the pulse current (i pulse ) applied to the electrostatic precipitator.

5. A system according to claim 1 , characterized in that said a clamping circuit ( 11 , 12 , 13 ) connected to the junction between the storage capacitor ( 7 ) and the first power supply ( 1 ).

6. A system according to claim 5 , characterized in that said clamping circuit comprises a diode ( 11 ) in series with a capacitor ( 12 ) and a resistor ( 13 ) in parallel with the diode ( 11 ).

7. A system according to claim 1 , characterized in that said a clamping circuit ( 60 , 61 , 62 ) is connected to the junction between the storage capacitor ( 7 ) and a primary winding of a transformer ( 9 ), said clamping circuit comprising a series connection of a damping resistor ( 60 ), a clamping diode ( 61 ) and a capacitor bank ( 62 ).

8. A system according to claim 7 , characterized in that said clamping circuit moreover comprises a DC power supply ( 63 ), a charging resistor ( 64 ), a transistor ( 66 ), a discharging resistor ( 65 ) and a reference diode ( 67 ).

9. A system according to claim 1 , characterized in that a snubber circuit ( 14 ) is connected in parallel to said switching device ( 5 ) and said anti-parallel rectifier device ( 6 ).

10. A system according to claim 1 , characterized in further comprising a bias network connected to a primary winding of a transformer ( 9 ), wherein said bias network comprises a voltage source ( 15 ), a limiting resistor ( 16 ) and a bias choke ( 17 ).